Cent os 7 Error downloading packages: 解决方法

yum一直用的好好地，今天安装NTP 突然报了一个错：

Error downloading packages:
  autogen-libopts-5.18-5.el7.x86_64: [Errno 256] No more mirrors to try.
  ntp-4.2.6p5-28.el7.centos.x86_64: [Errno 256] No more mirrors to try.
  ntpdate-4.2.6p5-28.el7.centos.x86_64: [Errno 256] No more mirrors to try.

 

网上查了查，需要清除缓存：

yum clean cache

yum makecache

结果又报了一个错：

已加载插件：fastestmirror
Determining fastest mirrors
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误"


 One of the configured repositories failed (未知),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
        or
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64

碰到这个错误。。。

换了yum源，改dns，网上的方法基本都试了一遍都没用

心态炸了

 

然后换了个思路，准备修复网络问题，结果是 GW 出了问题。。。

CentoOS7 minimal 出现ping: unknown host www.baidu.com解决办法：

• 修改 （vi /etc/sysconfig/network-scripts/ifcfg-eth0） 
  

• 重启网络 （systemctl restart network.service（或 service network restart））

• 查看 （cat /etc/resolv.conf ） 
  

  注意：不要在 /etc/resolv.conf 直接添加图片中的内容，CentOS7 重启网络会把 /etc/sysconfig/network-scripts/ifcfg-eth0 的DNS内容重新赋于到 /etc/resolv.conf 中

  此时可以尝试 ping www.baidu.com（若仍然ping不通执行继续执行）

• 差看路由表（netstat -rn） 
  

• 增加网关（route add default gw 192.168.175.1） 
  

                                                                                               GW 问题解决方案转自 -- zz657114506